1. Field of the Invention
The present invention relates to magnetic tape recording and reproducing apparatus for recording and reproducing digital signals of still picture data by using a magnetic tape as recording medium.
2. Description of the Related Art
One of the recording and reproducing apparatuses, hitherto known is a digital recording and reproducing apparatus for converting a sound signal into a digital signal, recording it into a magnetic tape, and converting the digital signal recorded in the magnetic tape back to the sound signal, and reproducing it.
In the case of this digital recording and reproducing apparatus, when converting the sound signal into a digital signal and recording into the magnetic tape, the information for correction of error can be simultaneously recorded as subsidiary information, and therefore if a part of the recorded information is missing. The missing portion can be reconstructed, and therefore the original sound can be reproduced at high fidelity, and reproduction of sound at an extremely low noise level is realized at the same time.
In such conventional digital recording and reproducing apparatus, in certain products, it is allowed to select, as its mode of action, either the two-channel mode for setting two channels for individually recording two types of sound signal in the magnetic tape, or the four-channel mode for setting four channels for individually recording four types of sound signal in the magnetic tape.
Of them, in the two-channel mode, two types of sound signals corresponding to two speakers located at the front left side and front right side of the listener are recorded in the magnetic tape, while in the four-channel mode, four types of sound signals corresponding to four speakers located at the front left side, front right side, rear left side and rear right side of the listener are recorded.
Additionally, in the case of the four-channel model, it has been also known hitherto to record sound signals in two channels, and still picture video signals in the remaining two channels, so as to reproduce the sound signal and video signal simultaneously from one magnetic tape.
In this system, for example, image memories are prepared to record the still picture video signals of one screen, and when recording, the video signals for one screen are converted into digital signals in an analog-to-digital (A/D) converter before being recorded in the magnetic tape, and are sequentially written once in one of the two image memories, and then the digital video signals for one screen are read out from the image memory, and recorded in two channels of the magnetic tape.
At this time, the sound signals supplied parallel to the video signal are also converted into digital signals in another D/A converter, and are sequentially written into the remaining image memories, and read out and recorded in the magnetic tape. As a result, in the magnetic tape, the video signals for one screen, and the narration or other sound signals corresponding to the screen are recorded simultaneously.
When reproducing, on the other hand, the digital video signals for one screen being read out from the magnetic tape are once written sequentially into one of the image memories, and after completion of writing, the video signals for that one screen are sequentially read out from that image memory, and the video signals being read out are converted back to the original analog video signals in a digital-to-analog (D/A) converter, and reproduced.
At this time, also, parallel to the digital video signals, the digital sound signals are read out from the magnetic tape and are converted into analog sound signals in D/A converter, and reproduced. As a result, when the still picture video signals for one screen are reproduced, the narration or other sound signals corresponding to the still picture are reproduced simultaneously.
In such conventional digital recording and reproducing apparatus, it does not matter when recording and reproducing video signals and sound signals of the NTSC (National Television System Committee) system are used as still picture data, but the following problems occur when recording and reproducing the video signals of the PAL (Phase Alternation by Line) system.
The phase repetition characteristic of the scanning lines in the video signals of PAL system is as follows: supposing the beginning of the first field, or the first scanning line to be in positive phase, the end of the first field, or the first half of the 313th scanning line is in positive phase, and the beginning of the second field, or the second half of the 313th scanning line is also in positive phase, and the end of the second field, or the 625th scanning line is also in positive phase.
Accordingly, the first scanning line of the third field begins at negative phase, and the end of the third field, or the first half of the 313th scanning line is in negative phase, the beginning of the fourth field, or the second half of the 313th scanning line is in negative phase, and the end of the fourth field, or the 625th scanning line is also in negative phase.
In order to record and reproduce the video signal of the PAL system correctly as still picture data, it is necessary to record continuous video signals for at least four fields as one unit as shown in FIG. 1. More specifically, when repetitively reproducing the continuous video signals for four fields, the number of scanning lines of the scanning line period (from the 622nd scanning line to the seventh scanning line) in phase face to face across the vertical synchronizing signal portion in the section from the last portion of the video signals of the fourth field until the first portion of the video signals of the next first field shown in FIG. 1(1) is 10, the number of scanning lines of the scanning line period (from the 309th scanning line to the 319th scanning line) in phase face to face across the vertical synchronizing signal portion in the section from the last portion of the video signals of the first field to the first portion of the video signals of the next second field shown in FIG. 1(2) is 10, the number of scanning lines of the scanning line period (from the 621st scanning line to the sixth scanning line) in phase face to face across the vertical synchronizing signal portion in the section from the last portion of the video signals of the second field until the first portion of the video signals of the next third field shown in FIG. 1(3) is 10, and the number of scanning lines of the scanning line period (from the 310th scanning line of the 320th scanning line) in phase face to face across the vertical synchronizing signal portion in the section from the last portion of the video signals of the third field until the first portion of the video signals of the next fourth field shown in FIG. 1(4) is also 10.
Therefore, in the conventional digital recording and reproducing apparatus, regarding the image memories for temporarily storing the still picture video signals before recording on the magnetic tape, only image memories of memory capacity for one screen, that is, two field are prepared, and when recorded and reproduced by taking in one screen portion of the video signals of the PAL system in this digital recording and reproducing apparatus, the phases of the scanning lines are matched on each screen, but the reproduced still picture is not colored, and other adverse effects are also brought about.
Additionally although, the method of converting the video signals of the
system into compound signals of the luminance signal and color difference signals, and writing into the image memories may be considered as a measure for solving the above problems, it requires complicated converting circuits, and it leads to new problems such as increase of cost.